[C320-list] Hatches and Portlights and Deadlights...oh my...

[Jeff Hare]

Hi Troy, 

By deadlights, I assume you mean the two long smoked windows in the galley / head?  If you mean the aft cabin porthole and the main cabin portholes, these probably clamp in place once the inner trim ring is removed.  But I suspect you mean the former...

We use VHB quite a bit installing keder welt track. It's great stuff. The problem you'll likely face is that while VHB is great for holding materials together, most long-term applications involve bonding two non-transparent materials which protect the adhesive and (typically) foam structural core of the tape. In this case, since you're bonding a semi-transparent surface to fiberglass, there is likely to be long-term UV exposure on the glass side of the adhesive (what little UV makes it through the smoked Acrylic). I think this is a case where VHB might have met its match. But the tech department at 3M has answered questions for me in the past and may help you here. I suspect that you'd really need to use polysulfide or whatever the factory recommends.  

Cheers!
-Jeff Hare

PS: when I mill acrylic or polycarb, I typically cut slightly oversized parts using hand held router with a deep V bit and a ~1/4" oversized collar that and use many passes scoring deeper until I have a blank that's slightly larger than finished size. Then I use a durable spiral down-cut bit to bring it to finished size. Whenever I've tried to just mill that in one pass I get chipping and micro-cracks.  Just my preference though... 😊

-----Original Message-----
From: C320-list <c320-list-bounces at lists.catalina320.com> On Behalf Of Troy Dunn
Sent: Friday, November 20, 2020 6:13 PM
To: C320-List at catalina320.com
Subject: [C320-list] Hatches and Portlights and Deadlights...oh my...

The threads on the original poster's question about deadlights (the fixed, non-opening 'windows' in the galley, head, salon, etc.) vs. non opening portlights vs. opening portlights (typically Lewmar) vs. hatches (typically Bomar on older hulls and Lewmar on newer) was getting difficult to follow and lots of the information in there could be misleading depending on which item you are trying to fix and what year your boat is.

For all of these items, please be aware that the preferred material of boat builders is cast acrylic, not polycarbonate (aka Lexan) and not extruded
acrylic.   Polycarbonate while intially stronger is an inferior material
for applications in sunlight due to UV degradation.   Cast acrylic is the
best product and it machines readily and quite nicely.

  I am currently in the process of replacing my forward trapezoidal hatch
with a new cast acrylic lens.   I bought the material from  estreet
plastics and will use the old lens as a template for the new one.  I will
post up some pictures on the process when I'm done.   I already replaced
the salon and head lenses using lenses bought from Catalina direct.    The
Catalina direct price is steep for what you are getting, so I figured I
would attempt to build one myself and see how this goes.   For price
comparison know that you could obtain enough acrylic for all three hatches for about $100 out the door inclusive of shipping.  This of course assumes you have a router table or CNC machine available for your use.

On the topic of dead light replacement, I have seen videos and diagrams of a frame that holds weight and pushes against the deadlight with legs braces
against the bulwark (aka toe rail).   This is the old school approach that
uses normal marine sealants.   I would be curious to hear if anyone has
gone the VHB double sided tape route.   That could potentially eliminate
all the fussing with weights etc.   alternatively if one didn’t trust the
UHB, you could run a thin inside gasket of UHB tape for holding power and a
plain sealant on the outer edge.   I know how crazy it sounds to 'just tape
your windows in place'.  But honestly I have used Sailrite's 3M SNADs which also use VHB tape and the holding power is pretty amazing.

For normal portlights there are already tons of good articles here already so I won’t dive back into that pond.

Troy Dunn
Hull #514